Well tool shock absorber



y 1968 J. E. STACHOWIAK 3,381,780

WELL TOOL SHOCK ABSORBER Filed April 1, 1966 ATTORNEY Unite 3,381,788 Patented May 7, 1968 3,381,780 WELL TOOL SHOCK ABSGRBER John E. Stachowiair, Houston, Tex., assignor, by mesne assignments, to Schlumherger Technology Corporation, Houston, Tex., a corporation of Texas Filed Apr. 1, 1966, Ser. No. 539,393 Claims. (Cl. 188-86) ABSTRACT OF THE DISCLQSURE The particular embodiment described herein as illustrative of one form of the invention in shock absorbers includes an elastomeric member in a housing, the member forming a working chamber and a passageway in communication with the working chamber. An actuator extends into the housing and engages the member. In response to kinetic energy of a moving body, the actuator can compress the elastomeric member which functions to displace hydraulic fluid from the working chamber into an auxiliary chamber via the passageway. In response to compression of the elastomeric member, the flow area through the passageway is progressively decreased while kinetic friction between the elastomeric member and housing is progressively increased, thereby providing a resultant variable damping coefficient such that the device will impart a substantially constant rate of deceleration to the moving body.

This invention relates generally to well tools and more particularly to a device for preventing the shock loads which can be developed during the operation of a formation testing tool from damaging various parts thereof,

In evaluating a well formation for either its commercial prospects or its condition after remedial work, it is the usual practice to make a temporary completion of the well. A well tool of the type shown in the 1966- 1967 General Catalogue of Johnston Testers at p. 2894 can be used for this purpose. Such tools are generally comprised of a packer or packers to isolate the interval to be tested, a test valve assembly for selective flow control, a bypass valve to aid in running-in and retrieval of the tool, and one or more pressure recorders for recording pressure changes in the well bore. The test valve assembly is part of a removable center section which can be retrieved and rerun through the tubing when multiple well zone operations are necessary. One or more pressure recorders are attached to the lower end of the removable test valve assembly, a typical pressure recorder being shown in US. Patent No. 2,816,440 to Garrison, entitled, Tension Type Pressure Recorder.

While running the tools into a fluid-filled well conduit the test valve is closed so that the tubing string above the valve is at a lower pressure than the hydrostatic mud pressure. This creates a buoyancy effect or flotation force acting upwardly on the tool. When the packer is set, the bypass closed and the test valve opened, the buoyancy effect is suddenly lost and a substantial shock load can be imparted to various parts of the tool, including the aforementioned pressure recorders which can be damaged by such shock loading because they usually include intricate clock mechanisms which rotate thin metal charts on which well fluid pressure changes are recorded.

It is accordingly the principal object of the present invention to provide a device for dissipating the energy developed during such shock loading so that tool damage which can be caused hereby is substantially minimized.

Broadly described, an apparatus which embodies the principles of the present invention comprises a case or housing having first and second chambers therein adapted to contain a hydraulic fluid, a passageway providing communication between the chambers, means including an elastomeric sleeve adapted to be compressed longitudinally of its length and expanded radially thereof for displacing hydraulic fluid from one chamber to the other via the passageway, the flow area through the passageway being variable responsive to compression and expansion of the elastomeric sleeve, and means for actuating the displacing means.

The novel features of the present invention are set forth with particularity in the appended claims. The present invention, both as to its structural organization and its operation, together with further objects and advantages thereof, may be best understood by way of illustration and example of one embodiment when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a longitudinal section view of apparatus which embodies the principles of the present invention.

FIG. 2 is a cross section taken on line 2-2 of FIG. 1; and

FIG. 3 is a cross sectional view similar to FIG. 2 and illustrating the progressive decrease in flow area through the passageway during operation of the device.

Referring to FIG. 1, a cylindrical case or housing 10 receives. a rod 11 for reciprocating movement therein. Slidably carried by the rod 11 is an elastomeric sleeve 12, the sleeve being received between two compression rings 13, 14 one of which abuts against a shoulder 15 formed by a reduced-diameter portion 16 of the rod and the other abutting against the shoulder 17 provided by a nut member which is threadedly coupled to an end portion of the rod.

The upper end of the case 10 is closed by a cap or closure member 18 which is secured to the case by threads 20 or other suitable means. A seal element 21, for example an O-ring, pressure seals the threaded joint. The closure member 18 has a centrally located opening 22 which is sized to slidably receive the rod 11. An O-r-ing 23 or other suitable sealing element is positioned in an annular groove in the closure member 18 to fluidly seal against the outer surface of the rod 11. A counterbore 24 in the closure member 18 is of larger diameter than the rod 11 to laterally space the inner wall of a portion of the closure member away from the outer surface of the rod 11 to provide an annular auxiliary chamber 25. A fill-up port 26 through the Wall of the closure member 18 permits hydraulic fluid to be introduced into the interior of the case 11) and a plug 17 sealably closes the port.

An intermediate portion 28 of the case 10 has an enlarged bore to provide an internal annular shoulder 30. The lower compression ring 14 normally abuts against the shoulder 39 to hold the lower end of the elastomeric sleeve 12 immovable relative to the case 18 in response to downward movement of the rod 11. The upper compression ring 13 abuts the end face 31 of the closure member 18 to hold the upper end of the sleeve 12 immovable relative to the case 10 in response to upward movement of the rod.

The el-astomeric sleeve 12 has a bore 32 therethrough which is sized for sliding reception on the reduced portion 16 of rod 11. The sleeve is of variable wall thickmess, the thinnest portion 33 being intermediate the length of the sleeve and the wall thickness gradually increasing from the portion 33 toward either end, thereby laterally spacing an outer surface of the sleeve 12 from the inner Wall surface of the case to provide an annular working chamber 34 therebetween. As was previously mentioned, each end of the sleeve abuts against a respective compression ring 13, 14.

Extending from points near the mid-portion 33 of the sleeve 12 toward either end thereof are peripheral grooves or slots 3535, 36-36 which provide passageways for communicating the working chamber 34 with the upper auxiliary chamber and a lower auxiliary chamber 37 below the end of the rod 11. The bottom of each groove lies in a plane substantially parallel to the longitudinal axis of the sleeve 12. Cross sectional details of the sleeve and peripheral grooves are shown in FIG. 3.

The upper compression ring 13 has radially cut slots 3838 therein which are maintained in alignment with the grooves -35 by a pin 40 reecived in both the compression ring and the sleeve. The grooves 36-36 extending from the mid-portion of the sleeve to the lower end thereof are likewise aligned with radially cut slots 4141 in the lower compression ring 14 to provide communication *between the working chamber 34 and the lower auxiliary chamber 37.

The lower auxiliary chamber 37 is closed by a balance piston 42 which is slidably received in the lower bore of the case 10. An O-ring 43 or other suitable sealing means fluidly seals between the balance piston 42 and the inner Wall of the case 10. The lower end portion 44 of the case 10 is internally threaded at 45 for coupling to the upper end of the pressure recorder (not shown). At least one lateral port 46 through the wall of the case below the balanced piston 42 permits fluid pressure externally of the case to be transmitted into the interior of the case and via the balance piston 42 to the fluids within the aforementioned chambers 37, 34, 25 to balance the various parts of the system against the hydrostatic or submergence pressures in which the shock absorber :may be immersed. Also, the balance piston 42 permits volumetric changes within the various chambers due to movement of the rod 11 and due to well bore temperature variations. Moreover, the piston 42 closes off the chambers 37, 34 and 25 from well bore fluids and prevents contamination of the hydraulic fluid by same, as well as preventing trash or other debris in the well from entering into the interior of the device.

The upper end portion of the rod 11 has an enlarged section 50 to provide an annular shoulder 51 which limits downward movement of the rod within the case 10. Above the enlarged section 50 is a threaded portion 52 for coupling to the lower end of the removable center section (not shown) of a formation testing tool.

In operation, the parts are assembled as shown in the drawings and the upper threaded portion 52 of the rod 11 is connected to the removable center section of a formation testing tool as above dscribed and the lower end 44 of the case is coupled with the upper end of a pressure recorder. A suitable hydraulic fluid is introduced into the chambers 25, 34, 37 via the fill-up port 26. When the formation testing tool is lowered into a fluid-filled well bore, the hydrostatic head of the well fluids is transmitted via the lateral port 46 to the balancing piston 42 and consequently to the hydraulic fluids in the chambers to pressure balance the device.

When the test valve for the testing tool is opened with a consequent loss of buoyancy, the removable center section which contains the test valve will jump downwardly and impart shock loading to the rod 11. Due to such loading, the rod will move downwardly with respect to the case and the upper compression ring 13 will approach the lower compression ring 14, thereby transmitting compressive forces to the elastomeric sleeve 12. As the sleeve 12 is compressed, it will cold flow and expand radially into the working chamber space and displace the hydraulic fluid from the working chamber 34 into the upper auxiliary chamber 25 via the grooves 35--35 in the periphery of the sleeve. Furthermore, as the sleeve expands radially, the flow area through the grooves 3535 will be progressively decreased because of the tendency of the elastomeric material of the sleeve to cold flow into the groove space as shown in FIG. 3. The consequent increased throttling of fluid flow through the grooves meters the flow in a manner to vary the hydraulic damping coeflicient as a function of the rod stroke.

Also, as the sleeve expands radially, it progressively tends to pack ofl? against the inner wall of the case, and the unit pressure exerted by the sleeve on the case wall builds up, thereby progressively increasing the kinetic friction between the sleeve and the case wall. The kinetic friction build-up also provides a damping coeflicient which varies as a function of the rod stroke. The combination of increased throttling of fluid flow through the grooves 35-35 and the build-up of kinetic friction between the sleeve and the case wall yields a resultant variable damping coeflicient such that the force which resists the motion of the rod 11 is essentially constant throughout the complete rod stroke. Consequently, a substantially constant rate of deceleration is imparted thereby to a moving load, a feature which is highly desirable in shock attenuating devices.

The inherent resiliency of the elastomer material of the sleeve 12 will cause the sleeve to return to its original shape and the rod 11 and the case 10 to return to their original relative positions. No sudden rebounding effect is present because the hydraulic fluid displaced into the auxiliary chamber 25 will be metered back into the working chamber 34, the metered flow occurring through a progressively increasing flow area of the grooves or slots 35-35.

It will be appreciated that the apparatus shown in the drawing is double acting, e.g., if a moving load should cause movement of the rod 11 upwardly with respect to the case 10, variable hydraulic damping will occur due to fluid displaced from the working chamber 34 into the lower auxiliary chamber 37 via the lower peripheral grooves 36-36 in the sleeve, with like friction damping forces acting in a direction opposite to those above described. It will be understood, however, that although the invention is shown embodied in a double acting device, certain or all of its features might be employed in other types of energy dissipating devices and it is not intended to limit the invention to the first named type.

Apparatus has been disclosed which provides effective energy dissipation for the shock loading which can be developed during the operation of a formation testing tool. It has been found that tool damage due to such shock loads has been substantially minimized to the unique features of the subject invention. Since certain changes and modifications may be made in the disclosed apparatus without departing from the scope of the inventive concept involved, it is intended that all matter contained in the foregoing description and shown in the attached drawings shall be interpreted as illustrative and not in a limited sense.

Iclaim:

1. A shock load attenuating device comprising:

a casing forming a cylinder, said casing having a first chamber therein;

a generally tubular elastomer member in said casing,

said member having an outer surface thereof laterally spaced from the internal wall surface of said housing to define a second chamber, said chambers containing a hydraulic fluid;

passageway means providing communication between said first and second chambers; and

means for compressing said elastomeric member whereby radial expansion thereof is effective to displace the hydraulic fluid from said second chamber into said first chamber via said passageway means, the compression and expansion of said member acting to progressively decrease the flow area through said passageway means and to progressively increase the unit pressure exerted by the member on the internal walls of the cylinder.

2. Apparatus for dissipating the kinetic energy of a moving body comprising: a housing; elastomeric means in said housing forming a. first chamber and a passageway in communication with said first chamber, said first chamber containing a hydraulic fluid; a second chamber in communication with said passageway; an actuating means extending into said housing movable relative thereto and engaging said elastomeric means to transmit compressive force thereto in response to kinetic energy of a moving body to effect deformation of said elastomeric means, whereby deformation of said elastomeric means efiects displacement of hydraulic fluid from said first chamber into said second chamber via said passageway and progressive decrease in How area through said passageway, said actuating means including a longitudinally extending rod, said elastomeric means being deformable radially outwardly of the axis of said rod upon movement of said rod relative to said housing, said elastomeric means being a generally tubular member slidably mounted on said rod; and coengageable means between at least one end of said tubular member and said housing for preventing movement of said one end relative to said housing during deformation of said tubular member.

3. Apparatus for dissipating the kinetic energy of a moving body comprising: a housing; an elongated elastomeric means in said housing forming a first chamber and a passageway in communication with said first chamher, said first chamber containing a hydraulic fluid; a second chamber in communication with said passageway; means for preventing movement of one end of said elastomeric means in said housing in one longitudinal direction; and actuating means extending into said housing and movable in said longitudinal direction, said actuating means including means engaging the other end of said elastomeric means to transmit compressive force thereto and effect deformation of said elastomeric means in response to kinetic energy of a moving body, said deformation effecting displacement of hydraulic fluid from said first chamber into said second chamber via said passageway and progressive decrease in flow area through said passageway.

4. The apparatus of claim 3 wherein said actuating means comprises a rod, said elastomeric means being deformable axially and radially with respect to said rod by said compressive force.

5. The apparatus of claim 3 further including means for balancing said actuating means against the submergence pressures of fluids in which the apparatus may be immersed, and for permitting volumetric changes within said housing during movement of said actuating means.

References Cited UNITED STATES PATENTS 2,212,759 8/1940 Tea 188-129 X 2,752,149 6/1956 Forcellini 18886 X 2,856,035 10/1953 Rohacs 188-100 X 3,109,520 11/1963 Vossieck 18886 X FOREIGN PATENTS 1,055,443 10/ 1953 France. 1,083,043 6/1954 France.

MILTON BUCHLER, Primaly Examiner.

G. E. A. HALVOSA, Assistant Examiner. 

